Nowadays, as polarizing films, generally, a polyvinyl alcohol base film (PVA film) in/on which iodine is adsorbed and oriented, a PVA film in/on which a dichroic dye is adsorbed and oriented, and the like are known. Such a polarizing film is usually used in the form of a polarizing plate comprising the polarizing film and a protective film adhered to at least one surface, preferably to both surfaces of the polarizing film.
Among those polarizing films, an iodine type polarizing film is usually produced by dipping a PVA film in/on which iodine is adsorbed and oriented in an aqueous solution containing boric acid and widely used as a part of a liquid crystal display since it has a higher light transmittance and a higher degree of polarization, that is, a better contrast than the dyestuff type polarizing film.
In these years, with the expansion of the application fields of liquid crystal displays and the progress of the peripheral technologies, the requirements for the optical properties and performances of the polarizing plate become higher and higher. That is, in the case of liquid crystal displays which are used outdoors or require low electricity consumption, polarizing films having high transparency and a high degree of polarization, that is, a high contrast are required. However, the currently available iodine type polarizing films do not necessarily satisfy those requirements sufficiently.